In conventional gas-operated engines, gaseous fuel, such as LP fuel or natural gas, is fed through a pressure regulator to an air/fuel mixer or carburetor. The pressure regulator includes a spring-biased diaphragm that is operated by engine intake air pressure, and that, in cooperation with a pressure regulating flow control valve, functions to feed gas at constant pressure to the mixer. The mixer functions to mix the gaseous fuel with air, and to feed the mixture to the engine intake manifold for transmission to the cylinder intake ports. In engine fuel control systems of this type, it is difficult to obtain optimum fuel flow over a wide range of operating conditions due to the design, calibration and maintenance requirements of the various mechanical components. Furthermore, fuel pressure does not achieve the necessary level to allow control by fuel injection and other conventional techniques employed in conjunction with gasoline engines.
Accordingly, several prior art fuel control systems have been proposed to provide a system for electronically controlling fuel flow to the mixer of a gas-operated engine so that engine operation can be electronically controlled by a microprocessor-based ECU or the like responsive to various engine and other parameter signals, and thereby achieve optimum fuel flow over a wide range of operating conditions. Examples of such prior art systems are disclosed in U.S. Pat. Nos. 4,449,509 and 5,117,798. which are incorporated by reference. These prior systems provide a solenoid motor having a linear actuator that is coupled through the housing of the pressure regulator to the main biasing spring for the regulator valve structure to thereby supplement the manifold vacuum sensing regulator diaphragm of the regulator by further varying the biasing force exerted by the valve-biasing spring. In this way, the primary spring-controlled operation of the regulator can be control modulated electronically, either entirely or supplemental to engine manifold pressure fluid/mechanical modulation.
More particularly, these prior art fuel control systems for delivering gaseous fuel from a high pressure source serially through a diaphragm-type pressure regulator and an air/fuel mixer to a gas-operated engine include at least one sensor for operative coupling to the engine to provide at least one electronic sensor signal responsive to a selected engine operating parameter or condition. An electronic control unit is responsive to the sensor signal(s) for providing a fuel control signal indicative of a desired quantity of fuel to be delivered to the engine in accordance with the sensed condition. A pressure regulator, for disposition between the fuel source and the fuel/air mixture, is responsive to the primary regulating valve spring, manifold vacuum and the fuel control signal for controlling delivery pressure of gaseous fuel to the mixer. The pressure regulator includes a housing having an inlet for connection to the fuel source and an outlet for connection to the mixer. A regulating valve is disposed within the housing and is spring-biased toward closure for controlling pressure and flow of fuel from the inlet to the outlet. A linear-actuator type solenoid force motor is built into the housing or located remote therefrom, and has a linear actuating coil for receiving the fuel control signal, and a linear-motion armature rod or piston that extends from the force coil into the housing to abut or engage one end of the valve biasing compression coil spring. The axially opposite end of the spring engages the valve-remote arm of a pivoted (first-class type) lever carrying the regulating valve at the end of its other arm. The armature rod operates to bodily move and/or vary the stress level of the spring for modulating control of the operative position of the valve via the valve biasing spring, and thereby is intended to control flow of gaseous fuel through the housing, as a function of the fuel control signal to the pressure regulator.
One disadvantage of the aforementioned fuel control systems of the foregoing prior art patents is that they mechanically input to the control system the effect of the at least one electronic sensor signal by applying the electromagnetically generated linear actuating force via a "soft" link, namely, the resilient valve biasing spring in the foregoing manner. Hence their mode of operation is to vary the urging force of the spring in order to achieve the cumulative spring and linear actuating coil biasing force tending to close the pressure regulating valve of the pressure regulator. On the other hand, manifold vacuum sensing by the pressure regulating diaphragm is rigid coupled by direct mechanical engagement with the valve-remote end of the valve operating lever. Hence a fluid-pressure differential-generated force exerted by the diaphragm is transmitted directly to the lever and via the lever only to the regulating valve member. Since the valve operating lever is essentially a rigid mechanical force transmitting member, it does not introduce an additional spring force or rate variable parameter into the system for controlling the pressure regulating valve operating forces.
However, the transmission of electromagnetically generated linear actuating force through the resilient valve biasing spring (that provides the main pressure regulating component of the pressure regulator) thus introduces the aforementioned "soft" element into the force transmitting linkage from the force coil linear armature rod, or piston, thereby adding another parameter and design complication to the system.
In addition to this "soft link" disadvantage, the systems of the two aforementioned prior art patents, due to the use of the valve biasing spring as a force transmitting element for inputting the additional electronic sensor signal input, do not lend themselves to retrofit modification of existing engine installations of fuel control system diaphragm-type, i.e., those pressure regulators in which the primary regulating spring action is modulated by changes in manifold vacuum sensed by the regulator diaphragm that acts directly on one end of a first class lever that moves the pressure regulating valve against the bias of a valve biasing spring acting between the valve lever and the regulator housing. Rather, the fuel control systems of the aforementioned prior art patents require that some or all of the components of the electronic control unit be incorporated by original design of the unit into the regulator structure and thus provided by incorporation at the point of the original manufacture of the regulator, thereby inherently rendering such fuel control systems unfit and/or uneconomic for application by retrofit to existing diaphragm-type pressure regulating housings.